Some wavelength converters generate converted light having a wavelength different from that of input light by using a nonlinear optical phenomenon, such as four-wave mixing, that occurs in an optical fiber. Non-patent Document 1 (M. Onishi, et al.: Proc. 23rd ECOC, 1997, vol. 2, p. 115) discloses that a desired wavelength conversion characteristic can be obtained by adjusting the wavelength of pump light, which is input to an optical fiber, in accordance with the zero-dispersion wavelength of the optical fiber. Non-patent Document 2 (K. Inoue, et al.: IEEE Photonics Technology Lett., vol. 6 (1994) 1451) discloses a wavelength-tunable light source that can be used for such a purpose. A wavelength converter using the wavelength-tunable light source has a complex structure and is expensive.
On the other hand, attempts have been made to obtain a desired wavelength conversion characteristic by adjusting the zero-dispersion wavelength of an optical fiber. For example, Non-patent Document 3 (M. Takahashi et al.: Proc. 32nd ECOC 2006 Th.1.5.1) discloses a method for shifting the zero-dispersion wavelength of a highly nonlinear fiber by stretching the fiber. However, Non-patent Document 3 does not disclose a specific method for applying tension to the fiber. In particular, a method for repeatedly changing tension is not examined in Non-patent Document 3.    Non-patent Document 1: M. Onishi, et al.: Proc. 23rd ECOC, 1997, vol. 2, p. 115.    Non-patent Document 2: K. Inoue, et al.: IEEE Photonics Technology Lett., vol. 6 (1994) 1451.    Non-patent Document 3: M. Takahashi et al.: Proc. 32nd ECOC 2006 Th.1.5.1.    Non-patent Document 4: T. Okuno, et al.: IEEE J. Select. Topics in Quantum Electron. Vol. 5 (1999) 1385.    Non-patent Document 5: T. Okuno, et al.: Electron. Left. vol. 39 (2003) 972.